If you’ve ever wondered whether someone looked at your email or not, you could use an email tracker. Gmail users can use Email Oracle, a free program from EmailOracle.com.

The old style was to ask an email recipient to click on a built-in receipt to show they got it. But EmailOracle embeds a tiny image in the email. When the recipient opens the email, that image is sent to EmailOracle’s computers. A little tracking window at the top of your Gmail screen then lets you know it’s been opened.

A similar service that works with Yahoo, Hotmail, AOL, Gmail and other online email systems is SpyPig, which is also free. It has some drawbacks: The chief one is that you have to manually load it every time you want to track an email. The nice thing is that the tracking image you add to an email can be invisible. Go to spypig.com for more info.